3 Answers
3

Quick clarification... "The average disk queue length is quite well documented in that it should not exceed 2 per CPU" should be "The average disk queue length is quite well documented in that it should not exceed 2 per spindle", but that common knowledge is not neccessarily true.

As I read your question, you want to know how many IOPS (IO's per second) is high for a hard drive. The answer is "when you have more than the drive supports". a 15K Seagate Cheetah supports many more IOPS than a 5400 RPM laptop drive. In your case, you have the drives setup as RAID 1 (which adds redundancy, but reduces the available IOPS as you write the same data twice).

The Disk Reads/Writes data in itself wouldn't (to me) make sense to have a specific high I/O defined, as hardware advances would render such things obsolete in short order. The key is looking for where things are causing delays, not simply what might be harmless but frequent disk activity.

Your disk manufacturer should provide info on the kind of IOPS you can expect to handle. Just as important as disk queue is sec/read and sec/write - anything more than 15-20ms sustained is probably gonna hurt.